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Simultaneous X-ray and optical observations of black hole X-ray binaries haveshown that the light curves contain multiple correlated and anti-correlatedvariation components when the objects are in the hard state. In the case of theblack hole X-ray binary, GX 339-4, the cross correlation function (CCF) of thelight curves suggests a positive correlation with an optical lag of 0.15 s andanti-correlations with an optical lag of 1 s and X-ray lag of 4 s. Thisindicates the two light curves have some common signal components withdifferent delays. In this study, we extracted and reconstructed those signalcomponents from the data for GX 339-4. The results confirmed that correlationand anti-correlation with the optical lag are two common components. However,we found that the reconstructed light curve for the anti-correlated componentindicates a positively correlated variation with an X-ray lag of ~ +1 s. Inaddition, the CCF for this signal component shows anti-correlations not onlywith the optical lag, but also with the X-ray lag, which is consistent with theCCF for the data. Therefore, our results suggest that the combination of thetwo positively correlated components, that is, the X-ray preceding signal withthe 0.15-s optical lag and the optical preceding signal with the 1-s X-ray lag,can make the observed CCF without anti-correlated signals. The opticalpreceding signal may be caused by synchrotron emission in a magneticallydominated accretion flow or in a jet, while further study is required tounderstand the mechanism of the X-ray time lag.

Extracting common signal components from the X-ray and optical light curves of GX 339-4: new view for anti-correlation